This invention is concerned with a method of sensing gobs of molten glass as they pass along a path which leads to a mould arrangement of a glassware forming machine. Although the invention is applicable to other types of glassware forming machine, it finds particular utility in glassware forming machines of the individual section type.
Glassware forming machines of the individual section type are well known and comprise a plurality of individual glassware forming units, called sections, which are arranged side by side to receive gobs of molten glass from a common source and to feed their output to a common conveyor. Each section has a parison mould arrangement at which gobs of molten glass are formed into parisons either by a pressing operation or by a blowing operation, a blow mould arrangement at which parisons are blown to the shape of the required container, transferring means for transferring parisons from the parison mould arrangement to the blow mould arrangement, and take-out means for removing completed containers from the blow mould arrangement. A machine may comprise six, eight, or ten sections and the sections receive gobs of molten glass in sequence from a common source. Thus, in the case of a six section machine, if a cycle of operation of the machine is represented by 360.degree., gobs are delivered at approximately 60.degree. intervals and the sections being their operation at approximately 60.degree. intervals so that, at any given time, all the sections are at different stages of their operation. The machine is controlled by timing means which causes the various events at each section to occur in the required sequence and synchronises the operation of the various sections. In older types of machines, the timing means comprises a timing drum carrying cams which continuously rotates so that the cams can operate valves in the required sequence. In more modern machines, the timing means is electronic and may involve one or more computers.
It has been recognised that it is desirable to provide signals indicating the arrival of the gobs of molten glass at the sections of the glassware forming machine. Such signals can be used to various purposes, for example for ascertaining the flight time of the gob from the common source to a particular section (the time varying from section to section because the distances involved are different), for synchronising the operation of the section with the actual arrival of the gob, or detecting the size of the gob from the length of the signal. To this end, in some machines, each section has been provided with a gob detector which is located so that it can detect the arrival of a gob at the parison forming arrangement of the section. In this way, it is possible to provide signals indicating the arrival of the gobs. The detectors used hitherto detect infra-red radiation emitted by the gob. However, the provision of such detectors in an environment made generally hostile by the proximity of molten glass requires that the detectors are protected from the environment and that wiring thereto is also so protected. Furthermore, accessability of the detectors in the event of a malfunction is limited unless the machine is closed down with a resulting loss of production. Furthermore, such infra-red detectors are susceptible to stray radiation which may cause erroneous readings.
It is an object of the present invention to provide a method of sensing gobs of molten glass as they pass along a path which leads to a mould arrangement of a glassware forming machine in which the possibility of erroneous readings by the detector used is reduced to a minimum.